JPH06290293A - Laser beam projector - Google Patents

Abstract

PURPOSE:To provide a certain fixed read enabling range regardless of an image forming position by varying the size of the aperture part of an diaphragm and adjusting the size of the aperture part of the diaphragm while being interlocked with a change in the image forming position of a lens system. CONSTITUTION:This device is provided with a laser light source 2 to emit laser beams, lens system 3 to condense the laser beams emitted from the laser light source 2, diaphragm 4 to limit the emission diameter of laser beams and focus control part 8 to change the image forming position of the lens system 3 by moving a single or plural lenses constituting the lens system. This diaphragm 4 can very the size of its aperture part, and is provided with an automatic control means to adjust the size of the aperture part while being interlocked with the change in the image forming position of the lens system 3. When the image forming position is close, the aperture of the 4 of the lens system 3 is made smaller and when the image forming position is far, the aperture of the diaphagm 4 of the lens system 3 is enlarged. Therefore, the read enabling range can be keep almost constant without being too small even when the image forming position is close or being too large when the image forming position is far.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam projector used in a scanning device which optically scans characters and bar codes.

[0002]

2. Description of the Related Art Conventionally, a laser beam projector using a laser has been used in bar code readers and character readers. In such a laser beam projector, in order to obtain a resolution higher than the diameter of the laser beam, it is necessary to focus the laser beam with a lens. And
Reading is performed by optically forming an image (focusing) with this lens.

However, it is difficult to actually read the bar code at the image forming position (focal position) of the lens, and the object to be read may shift back and forth from the image forming position. The allowable range of this deviation is called "readable range". For example, when reading a bar code, the readable range of the laser beam projector is about 10 cm if the minimum line width of the bar code is 0.2 mm.

[0004]

If the beam diameter narrowed by the lens (hereinafter referred to as "spot diameter") is too large, the resolution is lowered and the object cannot be read correctly. In addition, if the spot diameter is too small, it may not be possible to read the barcode correctly due to the lack of printing or stains on the barcode.

Therefore, it is desirable that the spot diameter can be freely adjusted according to the thickness of the bar code to be read. On the other hand, in order to deal with the case where the object to be read moves back and forth from the image forming position beyond the readable range, a method of adjusting the image forming position of the lens system (refer to Japanese Patent Laid-Open No. 1-175686) A method has been proposed in which a plurality of different optical systems are prepared and switched (see JP-A-1-189782 and JP-A-2-133891), but there remains a problem regarding the relationship between the image formation position and the readable range. ing.

That is, when the image forming position is set short, the readable range becomes inevitably shallow, and even when the image forming position is set long, the readable range becomes shallow. FIG. 2 is a graph showing this relationship, in which the horizontal axis represents the distance from the lens to the object to be read, and the vertical axis represents the beam diameter. The three beams are emitted from lenses having different image forming positions, and the beam A having the closest image forming position is the spot diameter D.
_A small, effective reading beam diameter D _S equal to or less than the range (readable range) L _a is made relatively narrow. On the other hand, the beam B having the intermediate image forming position has a medium spot diameter D _B and a relatively wide readable range L _b .
The beam C farthest from the imaging position has a large spot diameter D _{C and a} relatively narrow readable range L _c .

As can be seen from the graph of FIG. 2, the readable range is a function of the image formation position. However, it is desirable that the readable range be constant regardless of the image forming position for the person who actually uses it.
Therefore, it is a first object of the present invention to provide a laser beam projector that can obtain a constant readable range regardless of the image formation position.

Further, according to the present invention, the spot diameter can be freely adjusted according to the thickness of the line of the bar code or the like to be read, and thus a laser beam projector capable of accurately reading characters and codes is provided. The second purpose is to provide.

[0009]

[Means and Actions for Solving the Problems]

(1) A laser beam projector according to claim 1 for achieving the above object, is a lens including a laser light source for emitting a laser beam and a single lens or a plurality of lenses for condensing the laser beam emitted from the laser light source. A laser beam including a system, a diaphragm that limits the emission diameter of the laser beam, and a focus adjusting unit that can change the image forming position of the lens system by moving one or more lenses that form the lens system. In the projector, the size of the aperture of the aperture is variable, and the aperture is provided with automatic control means for adjusting the size of the aperture of the aperture in association with the change of the image forming position of the lens system.

When the image forming position of the lens system is changed, the size of the aperture of the diaphragm is not fixed as in the conventional case, but
If it is changed in conjunction with the image forming position, the readable range can be made almost constant. FIG. 1 is a graph in which the horizontal axis is the distance and the vertical axis is the beam diameter. It is shown that a beam b having a large emission diameter D ₀ and a beam a having a small emission diameter D are focused at different imaging positions. There is. Specifically, when the image forming position is close, the diaphragm of the lens system is reduced,
When the image forming position is far, the diaphragm of the lens system is enlarged. As a result, the readable range does not become too small even when the image forming position is close and does not become too large when the image forming position is far, and can be kept substantially constant. (2) The laser beam projector according to claim 2 has a laser light source that emits a laser beam, a lens system that includes a lens or a plurality of lenses that collects the laser beam emitted from the laser light source, and an emission diameter of the laser beam. And an aperture for limiting the aperture, the aperture having a variable aperture size,
A diaphragm control means for manually adjusting the size of the aperture of the diaphragm is provided.

Generally, the spot diameter w of the laser beam is
Assuming that the laser beam is a Gaussian beam,
F is the image forming position, the wavelength is λ, and the exit diameter at the lens position
To D ₀Then, w = fλ / πD₀ Required in (1).

From this, it can be seen that the spot diameter w and the exit diameter D ₀ are in inverse proportion to each other at the same image forming position. FIG. 3 is a graph in which the horizontal axis represents the distance and the vertical axis represents the beam diameter, and shows how the beam a having a large emission diameter D ₀ and the beam b having a small emission diameter D ₀ are respectively narrowed. According to the configuration of the invention, since the size of the aperture of the diaphragm is variable and the aperture control means for adjusting the size of the aperture of the diaphragm is provided, the size of the aperture of the diaphragm is adjusted by the aperture control means. By adjusting, the spot diameter of the beam can be arbitrarily selected. (3) The laser beam projector according to claim 3 further comprises output control means for changing the output of the laser light source according to a change in the size of the aperture of the diaphragm.

In the case of the laser beam projector according to the first or second aspect, the beam output intensity naturally changes because the emission diameter D ₀ changes, but the beam output intensity changes when reading characters or bar codes. Not preferable. When the beam intensity becomes weak, it is easily affected by noise and the reading performance deteriorates. When the beam intensity becomes excessive, there is a safety problem. Therefore, the output control means changes the output of the laser light source according to the change in the size of the aperture of the diaphragm. (4) In the laser beam projector according to claim 4, the diaphragm has a structure in which the horizontal width and the vertical width change independently, and the diaphragm control means independently adjusts the horizontal width and the vertical width. It is possible.

With this configuration, when the scanning direction is one direction, the same operation as the invention according to claim 3 can be achieved by adjusting only one of the beam diameters in the vertical and horizontal directions.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a laser beam projector is applied to a bar code reader will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the bar code reader but may be an optical character reader or the like. It should be noted in advance that it can be applied to a scanning device that optically scans a.

FIG. 4 shows a bar code reader 1 including a laser beam projector. The bar code reading device 1 includes a laser light source 2, a lens system 3, a diaphragm 4, a polygon mirror 5, a distance measuring unit 6, a diaphragm control unit 7, and a focus adjustment unit 8.
And an output control unit 9. Although a semiconductor laser is used as the laser light source 2, a gas laser such as a He—Ne laser may be used.

The output control section 9 has an electric circuit for changing the intensity of output light by changing the magnitude of the forward current of the semiconductor laser. The lens system 3 is the laser light source 2
The laser beam emitted from the lens is imaged at a certain point, and a combination lens such as 2 groups 2 elements and 2 groups 3 elements which suppress aberration is used, or one aspherical lens.

When a He-Ne laser or the like is used, the beam emitted from the laser is thin and does not spread. Therefore, it is preferable that the beam is once spread by another concave lens and then passed through the lens system 3. The lens system 3 is movable in the front-back direction with respect to the laser light source 2, and this movement is performed by driving from the focus adjusting unit 8. Specifically, the lens barrel is threaded, and the lens is moved by rotating the barrel or the outer periphery by a motor and a gear. The motor and the gear constitute a focus adjustment unit 8. This focus adjusting mechanism has a conventionally known structure, and is described in detail in JP-A-2-
It is disclosed in Japanese Patent No. 170290.

As shown in FIG. 5, the diaphragm 4 is formed by radially rotating thin metal pieces 40 used in a shutter of a camera or the like so that the central opening can be freely opened. Which is also controlled by the motor and gears. The motor and gear correspond to the diaphragm control unit 7. The structure of the diaphragm 4 is not limited to that shown in FIG. For example, as shown in FIG.
A large number of holes having different diameters may be formed in 1 and the disc 41 may be rotated to allow the beam to pass through any of the holes.

One of the advantages of providing the diaphragm control unit 7 is that the laser beam can be prevented from being accidentally emitted from the bar code reader 1.
For example, since a He-Ne laser is not easy to control electrically, it is kept oscillating for a certain period of time. For this reason, when the barcode reading device 1 is not used for a while, it is dangerous that the laser beam reflected by the polygon mirror 5 at rest is radiated to a certain point. Therefore, the diaphragm control unit 7 closes the diaphragm 4. By doing so, danger can be prevented and the life of the laser light source 2 and the driving motor of the polygon mirror 5 can be extended.

The laser beam that has passed through the diaphragm 4 is oscillated in one direction or in multiple directions by a polygon mirror 5 which is a scanning means, and is emitted toward an object to be read. In addition to the polygon mirror, a reciprocating mirror, a rotating prism, or a combination thereof with a fixed mirror can be used as the scanning means. The distance measuring unit 6 is a portion that measures the distance to the reading target, and as the distance measuring method, a conventionally known method such as a reflection optical type, a transmission optical type, or an ultrasonic type can be adopted. The distance information obtained by the distance measuring unit 6 is given to the aperture control unit 7, the focus adjustment unit 8, and the output control unit 9, respectively, and the aperture control unit 7 adjusts the aperture diameter D ₀ of the aperture 4 to adjust the focus. In the section 8, the image forming position of the lens system 3 is adjusted,
In the output control unit 9, the output of the laser light source 2 is adjusted.

In these adjustment methods, it is possible to calculate the adjustment value each time using a certain arithmetic expression, but in practice, it is preferable to use a table in which the distance and the adjustment value are associated and stored. It's quick and easy. The contents of the table can be determined by experimentally obtaining the optimum value in advance. It is possible to store some points in the table and use the intermediate value of the stored values for the intermediate distance.

Next, a specific adjusting method will be described. When the power switch is turned on with the light emission port of the barcode reading device 1 facing the reading target, the distance measuring unit 6 measures the distance to the reading target. Based on this distance information, the focus adjustment unit 8 moves a part or all of the lens away from the laser light source 2 by a predetermined distance when the reading target is near, and a part of or the lens when the reading target is far. All are brought close to the laser light source 2 by a predetermined distance. This allows the lens system 3
The image forming position of can be matched with the reading target.

At the same time, the aperture control unit 7 determines that the reading target
Is near, the diameter D of the opening ₀Open small, figure
The state of curve a shown in 1 is created. This allows you to read
Available range L_ACan be prevented from narrowing
To realize a bar code reading device 1 that is easy to use.
You can Also, the diameter D of the opening₀Becomes smaller
Since the beam extraction efficiency is reduced, the beam output must be kept constant.
Therefore, the output control unit 9 increases the output of the laser light source 2.

On the contrary, when the object to be read is far away, the diameter D _{0 of the} opening is widened and the curve b shown in FIG.
Create the state of. As a result, the beam emission efficiency can be increased, so that the output control unit 9 controls the laser light source 2
There is no need to increase the output of. Therefore, the power consumption can be reduced and the life of the laser light source 2 can be extended.

Next, another embodiment will be described. In this embodiment, it is assumed that the distance from the barcode reading device 1 to the reading target is substantially constant. The bar code reading apparatus 1 of this embodiment has substantially the same configuration as the bar code reading apparatus 1 of FIG. 4, but the difference is that the diaphragm control unit 7 can be manually driven. Specifically, the aperture diameter D ₀ is adjusted by manually rotating the metal piece 40 and the disc 41 that form the diaphragm 4.

Since the aperture diameter D ₀ can be freely adjusted, the spot diameter narrowed by the lens diameter can be freely adjusted according to the thickness of the bar code to be read,
Therefore, it is possible to prevent the reading accuracy from deteriorating due to the influence of chipping or stains on the printing due to the spot diameter becoming too thin. In this embodiment as well, the output efficiency decreases as the diameter D _{0 of the} opening decreases, so that the output control unit 9 controls the output of the laser light source 2 to increase in order to keep the beam output constant.

In the above two embodiments, the diaphragm 4 is
It may have a structure in which the horizontal width and the vertical width change independently. FIG. 7 is a front view of an essential part of the diaphragm 4 having such a structure in which four thin metal pieces are stacked, and a pair of upper and lower metal pieces 4 are provided.
2, 42 and the pair of left and right metal pieces 43, 43 are independently moved. This movement may be performed by a motor and a gear (not shown).

With such a structure, the beam can be focused only in the scanning direction of the object to be read,
The direction perpendicular to it can be expanded without necessarily squeezing it. Therefore, it is possible to maintain that the output of the laser light source 2 as a whole is kept constant by compensating that the output efficiency is lowered by narrowing one side and being compensated by widening the other side. Therefore, it is effective for a gas laser such as a He-Ne laser whose output control is difficult.

[0030]

As described above, according to the laser beam projector of the first aspect, the size of the aperture of the diaphragm is variable, and the aperture of the diaphragm is interlocked with the change of the image forming position of the lens system. The readability range can be made substantially constant by adjusting the size of the. Therefore, it is possible to realize a convenient laser beam projector that can obtain a constant readable range regardless of the image formation position.

According to the laser beam projector of the second aspect, the spot diameter of the beam can be arbitrarily changed by adjusting the size of the aperture of the diaphragm.
Therefore, it is possible to accurately read characters and codes having different line thicknesses. Further, according to the laser beam projector of claim 3, according to the change of the size of the aperture of the diaphragm,
Since the output of the laser light source can be adjusted, the beam output intensity can be made constant. Therefore, the reading conditions are stable and reliable reading can be performed.

Further, according to the laser beam projector of the fourth aspect, since the horizontal width and the vertical width of the aperture of the diaphragm can be changed independently, when the scanning direction is one direction, either the vertical or horizontal direction. Only one aperture needs to be adjusted.
Further, the beam output can be made constant as a whole by adjusting the diaphragms in the other directions at the same time. Therefore, the same effect as that of the invention of claim 3 is obtained without changing the output of the laser light source, and the drive control circuit of the laser light source becomes unnecessary.

[Brief description of drawings]

FIG. 1 is a graph showing how a beam with a large emission diameter and a beam with a small emission diameter are focused at different imaging positions.

FIG. 2 is a graph showing that the readable range is different for each of three beams having different imaging positions.

FIG. 3 is a graph showing how a beam having a large emission diameter D _{0 and} a beam having a small emission diameter are focused on different spot diameters at the same image forming position.

FIG. 4 is a block diagram showing a bar code reader including a laser beam projector.

FIG. 5 is a view showing a diaphragm formed by radially superimposing thin metal pieces.

FIG. 6 is a structural diagram of a diaphragm in which a large number of holes having different diameters are formed in a circular plate and the circular plate is rotated so that a beam is passed through one of the holes.

FIG. 7 is a front view of a main part of a diaphragm having a structure in which a width and a length are independently changed.

[Explanation of symbols]

 1 Bar Code Reader 2 Laser Light Source 3 Lens System 4 Aperture 8 Focus Adjuster 9 Output Controller

Claims (4)

[Claims] 1. A laser light source for emitting a laser beam, a lens system comprising a single lens or a plurality of lenses for condensing the laser beam emitted from the laser light source, a diaphragm for limiting the emission diameter of the laser beam, and the lens. In a laser beam projector provided with a focus adjusting means capable of changing an image forming position of a lens system by moving a single lens or a plurality of lenses constituting the system, the aperture has a variable aperture size. The laser beam projector further comprises automatic control means for adjusting the size of the aperture of the diaphragm in association with the change of the image forming position of the lens system. 2. A laser comprising a laser light source for emitting a laser beam, a lens system comprising a single lens or a plurality of lenses for condensing the laser beam emitted from the laser light source, and a diaphragm for limiting the emission diameter of the laser beam. In the beam projector, the aperture has a variable aperture size, and the aperture is provided with aperture control means for manually adjusting the aperture size of the aperture. 3. The laser beam projector according to claim 1, further comprising output control means for changing the output of the laser light source according to the change in the size of the aperture of the diaphragm. 4. The diaphragm has a structure in which the horizontal width and the vertical width change independently, and the diaphragm control means can independently adjust the horizontal width and the vertical width. The laser beam projector according to claim 1 or 2.